We have shown that the striking rise in protein synthesis observed after the fertilization of sea urchin eggs results from two processes. The first is the unmasking of messenger RNA molecules which are present in the egg in association with proteins (mRNPs) which make them unavailable for translation before the egg is fertilized. The second is the increased efficiency of the protein synthesis machinery following fertilization. We are investigating several aspects of these mechanisms. These are: 1. Analysis of the proteins which are associated with messenger RNA molecules in eggs and in embryos to determine the nature of the unmasking process; 2. The use of artificial activators to define the nature and timing of controls. Artificial activators allow us to experimentally uncouple unmasking from increased translational efficiency; 3. The characterization and use of cDNA clones of oogenetic mRNAs as probes for the recruitment of individual messenger species after fertilization.